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Home - General / All posts - Manifold 9: Crosshair Cursor behaviour when digitising
#14-Feb-18 04:27

I've spent some time in the manual and searching the forum, but I have not found an answer to my question about the behaviour of the crosshair cursor when digitising in Manifold 9.

I've been digitising new drawing layers based on images of maps. When I draw a new line the first node appears about 1 or 1.5 cm from the horizontal arm of the crosshair cursor. I find that this makes precisely digitising the underlying image a challenge.

Is this the normal behaviour of the tool, or am I missing a setting somewhere in the software?

Chris

steveFitz

208 post(s)
#14-Feb-18 06:52

Are you using a digitizing pen and tablet or a mouse?

If the former, does it need to be re-calibrated?

Dimitri


4,941 post(s)
#14-Feb-18 07:51

As a theoretical point, I suppose it might be possible to get such an effect if the projection for a given layer was specified in a grossly wrong manner. Even then, I'm not sure.

I just offer the above based on the general observation that when objects start appearing in wildly unexpected places the trouble is often a wrongly specified coordinate system. Never hurts to be sure that coordinate systems are correctly specified, so no harm done looking into that. :-)

adamw

8,037 post(s)
#14-Feb-18 09:39

Is that 1 or 1.5 cm of the screen distance? That is, you click a location and the system adds a coordinate 1 or 1.5 cm away from where you clicked? If so, could you please send your data (map with source image and target drawing)? If the data is sensitive, contact tech support (perhaps file a report for a potential bug: here is how).

If that's 1 or 1.5 cm of real Earth distance, perhaps that's a question of zoom used during digitizing (should zoom a bit more).

rk
271 post(s)
#14-Feb-18 10:05

If Map projection is different from Drawing projection then there is displacement.

Attachments:
Crosshair.mxb
crosshair_displaced.png

Dimitri


4,941 post(s)
#14-Feb-18 11:57

If Map projection is different from Drawing projection then there is displacement.

I've done this a zillion times and have never seen that issue when a map projection is different than the drawing, for example, the photo below, where the map is in pseudo mercator and the drawing is in lat/lon. Works perfectly every time. (the photo is a combination of two screenshots, one showing the Component pane and the other the "live action" editing..) To make photos in posts bigger, just click on them.

Could you post a screenshot of the Component panel of the Contents pane for your map with drawing layer?

If there is a problem with the way a coordinate system has been assigned, figuring out errors in workflow requires detailed, step by step descriptions of how you created what you are working with. Problems are frequently caused by the key differences in dialogs such as Assign Initial Coordinate System and Change Coordinate System.

Ah... one more idea. In cases of extreme mismatch between coordinate systems, like trying to show a highly local coordinate system overlaid on a "whole Earth" coordinate system like pseudo mercator, you can, indeed, get crazy effects. Normally such craziness happens if coordinate systems are wrongly assigned, but they can happen when coordinate systems are correctly assigned but a wildly inappropriate coordinate system has been used, or with wildly inappropriate parameters.

For example, Lambert Conformal Conic (LCC) is a sensible coordinate system but if you project a drawing into LCC centered on Kansas and you start clicking away at it as a layer in a map that uses Pseudo Mercator and is panned and zoomed to Zimbabwe, you're going to get some strange effects.

If you tell us more about what you've done, all details, we can help zero in beyond such very general discussion.

Attachments:
works_fine.png

rk
271 post(s)
#14-Feb-18 12:22

Could you try with .mxb from my previous post. Coordinate systems used are UTM zone 35N for map and UTM zone 32N for Drawing.

Attachments:
crosshair_displaced2.png

Bernd Raab33 post(s)
#14-Feb-18 12:34

I opened the mbx-file and found that the first node actually jumps off from the desired location whenever I start digitizing.

Then under the components pane I edited the map coordinate system to exactly the same EPSG 25832, then I edited the drawings coordinate system also to the same EPSG. After that the effect of jumping off is gone, digitizing works as it should. Hope this helps

adamw

8,037 post(s)
#14-Feb-18 15:38

The coordinate does jump if you are editing the drawing from the map, but that's because the coordinate system conversions are forced to be inaccurate by the choice of source and target coordinate systems.

Converting a location from UTM zone 32 to UTM zone 35 or vice versa is going to lose a lot of accuracy, that's in the nature of the formulae for TM. With the distance between the centers being as high as it is, there is no way for the coordinate not to jump.

If you set the coordinate system of the map to something that is reasonably accurate within the longitude interval of the UTM zone of the drawing - to lat / lon or to pseudo-Mercator or to Mercator (or, obviously, to the same UTM zone), etc - the coordinate stops jumping.

Dimitri


4,941 post(s)
#14-Feb-18 15:52

Yes... it is never a good idea to combine UTM zones. That would be an example of my "mismatch between coordinate systems" guess. For anyone who works with UTM coordinate systems, there is a useful discussion in the UTM topic (nice illustrations, too) under the UTM Zones should not be Combined heading.

rk
271 post(s)
#14-Feb-18 17:03

Thanks. I use UTM only recently and I didn't know how bad it is to combine zones. I knew how to make a sample because I once accidentally saw the displacement but didn't think much of it. Now I know why I saw it and that it indicates a problem.

#15-Feb-18 21:08

Thank you everyone for the comments and help.

It did indeed turn out to be a projection issue. I had loaded a LIDAR base layer in a particular UTM projection. When I created the new drawing layer it automatically assigned it a different UTM projection, but the right zone, and I didn't notice that happen. Once I changed the projection on the drawing layer everything worked out perfectly.

And just to answer one of the questions posted to me here. The mis-match in projections caused a 1.0-1.5 cm screen offset between the first node and the cursor.

Now that I have this resolved I will continue to happily digitise with speedy raster and LIDAR handling.

Cheers,

Chris

adamw

8,037 post(s)
#16-Feb-18 07:37

Happy to hear the issue is resolved (and was indeed related to a pair of projections that don't play well with each other).

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